Method of producing water-soluble products from black liquor lignin



Patented June 1, 1954 METHOD OF PRODUCING WATER-SOLUBLE PRODUCTS FROMBLACK LIQUOR LIGNIN Erich Adler, Lidingo, and Erik Karl MauritzHiigglund, Stockholm, Sweden, assignors to Svenska CellulosaforeningensCentrallaboratorium, Stockholm, Sweden No Drawing. Application December19, 1950, Serial No. 201,696

Claims priority, application Sweden December 22, 1949 19 Claims.

1 The present invention relates to a method for producing water-solubleproducts from black liquor lignin obtained by digesting hardwood, or

coniferous wood, or other lignocellulose containing materials, accordingto the soda or sulphate cellulose processes.

It is known that the lignin sulphonic acid obtained as a by-product inthe sulphite cellulose process has in many cases proved to be useful usifying and disper g agent, and also g an other purposes. condition forthis is amongst other things the solubility of the nin sul h id and itssalts in water or diluted acids. Contrary hereto, it has hitherto notbeen possible to use waste lignin from the soda and sulphate celluloseprocesses, hereafter called black liquor lignin, for similar purposes,owing to lacking water-solubility of this lignin.

In our copending application, Ser. No. 201,695, filed December 19, 1950,we describe and claim a process of rendering black liquor lignin solublein water and dilute acids. In this process black liquor li nin istreated with a sulfonating agent, such as sulfurous acid or a solublesulfite, to introduce sulfonic acid groups into the allphatic sidechains of the lignin molecule. The water-soluble products thus obtainedful for the aove-men nand similar purposes.

T It has been found that the sulfonating step of this acknowledgedcopending application can be facilitated and promoted by subjecting theblack liquor lignin to an oxidizing treatment in connection with thesulfonation.

Based on these discoveries, according to the invention, the black liquorlignin is first subjected to an oxidizing treatment and then to atreatment with a sulphonating agent, such as sulphurous acid or a saltthereof, or a substance which can give rise to the formation of any ofthe mentioned compounds. It is also possible to carry out the oxidizingtreatment and the sulphonation simultaneously. The black liquor ligninis not subjected to any preliminary special treatment with alkali beforethe conversion according to the invention and it may be used for thisconversion directly in the form in which it is obtained by thedigestion.

By means of the sulphonating treatment according to the invention whichmay be carried out in acid, neutral or, preferably, alkaline solution,the black liquor lignin is converted intov sulphonic acid derivatives,the -SOaH groups entearing the aliphatic side chain of the ligninmolecule, whereby water-soluble products are 2 produced. As sulphonatingagents preferably soluble sulphites are used, especially alkali metalsulphites and preferably sodium sulphite or, when working in acidsolution, also sodium bisulphite, but also the corresponding ammoniumsalts.

The oxidizing treatment may be carried out with any suitable oxidizingagents, preferably oxygen or oxygen delivering substances, suitably inalkaline solution. Due to the oxidizing of the lignin, the subsequentconversion with a sulphite takes place more rapidly and may be carriedout at a lower temperature. The oxidizing treatment may for example beaccomplished by passing air or oxygen into a solution of the blackliquor lignin at boiling temperature under normal pressure. If desired,the oxidation may be carried out in the presence of oxidation catalysts,such as salts of iron, copper and cobalt.

According to an embodiment of the invention the oxidizing andsulphonating treatment of the lignin material may be combined with atreatment with an aldehyde, preferably formaldehyde, or agents givingoff aldehyde. This treatment with an aldehyde is carried out after theoxidizing treatment has taken place, but may be performed either beforethe sulphonating treatment-suitab1y in alkaline solution-or at the sametime as the conversion with the sulphonating agent. In the former caseCH2OH groups are introduced into the lignin molecule in the aromaticnuclei thereof, more precisely in positions that are in orthoposition toa free phenolic hydroxyl group. When subsequently reacting such methylolderivatives with a sulphite, preferably in a medium having a weakalkaline reaction, said CH2OH groups are converted into CHzSOaH groups,and at the same time SO:-.H groups are introduced into the aliphaticside chain of the lignin molecule. These CH2S03H groups may also beformed in a single reaction stage, if the black liquor lignin-after theoxidizing treatment-is reacted with a mixture of formaldehyde and sodiumsulphite.

Further, it is possible to combine said reactions with each other insuch a manner that the black liquor lignin is first oxidized andsimultaneously or afterwards subjected to a heating with a sulphite inacid, neutral or, preferably, alkaline solution, thus introducing SO:H

groups in the aliphatic side chain of the lignin molecule, as indicated,whereupon the resulting product is reacted with an aldehyde, for exampleformaldehyde, in the presence of a sulphite,

till-\MINEK preferably in alkaline solution, whereby -CmSOzI-I groupsare introduced into the aromatic nuclei of the molecule and at the sametime the sulphonation in the aliphatic side chain is carried on to astill higher extent. A similar result is also obtained by firstreactingthe oxidized black liquor lignin with the aldehydesulphitemixture, for example formaldehydesodium bisulphite addition compound,and then subjecting the product thus obtained to a subsequentsulphonation by heating with a sulphite in acid, neutral or, preferably,alkaline solution.

When carrying out these combined reactions it is not necessary toisolate the product formed in the first conversion stage, but it may inmany cases be suitable, after the first stage has been accomplished, toadd directly to the reaction mixture the chemicals necessary for thesecond reaction stage, and then to "carry out said reaction stage.

The treatment with the sulphonating agent, for example a sulphite, or asulphite and an aldehyde (aldehyde-bisulphite addition compound), mayfor example be carried out within a temperature range of 50 to 200 Ci,suitably 80 to 170 C., preferably 100 to 160 0., when required underpressure. The quantity of sulphite used, calculated as anhydrous sodiumsulphite, may be 10 to 100% of the quantity of anhydrous lignin, and thequantity of aldehyde may be equivalent to the quantity of sulphite orlower, down to about 1 calculated on the quantity of the anhydrouslignin material. As already mentioned, the treatment is preferablycarried out in alkaline solution in which case the sulphonation isaccomplished in a shorter time, but in many cases it may also be toadvantage to work in acid solution.

By applying the present invention, it is possible to produce from blackliquor lignin sulphonic acid derivatives with varying content or numberof sulphonic acid groups. Thus, when oxidizing and directly convertingblack liquor lignin with sulphite solutions at higher temperature, inaccordance with the degree of acidity, the temperature and the time ofreaction chosen, one or sever SOaI-I groups per 5 methoxyl groups areintrduced into the lignin molecule. When reacting the oxidized blackliquor lignin with an aldehyde, with simultaneous or subsequenttreatment with a sulphite in the manner indicated, under formation ofCH2SO3H groups, likewise such a group enters per about 5 methoxylgroups.

Owing to the fact that direct sulphonation or sulphonation byformaldehyde-sulphite acts upon the lignin molecule at different placesand by applying the first mentioned or the last mentioned of these twoprincipal reaction types, or by combining said reaction types indifierent ways, as indicated above, it is possible to vary within widelimits the final content of sulphonic acid groups (SOaH groups and.CI-IzSOaH groups), in the reaction products, and as a consequence hereofalso the properties of the products. Thus, for example, it has beenproved that sulphonic acids, produced by oxidizing and converting blackliquor lignin with formaldehyde-sulphite addition compound, are solublein water and acetic acid, but they can be precipitated by dilute mineralacids. On the other hand, higher sulphonated products, which may beobtained for example by oxidizing and then reacting black liquor ligninfirst with formaldehyde-sulphite addition compound in a weak alkalinesolution at'80 to 100 C. and then with a sulphite at a pH of 9 and about130 C., are also soluble in dilute mineral acids, and areprehardening-promoting and strength-increasing cipitated from theiraqueous solutions only at a comparatively high concentration of mineralacid.

In this connection it may be pointed out that it is not necessary to useisolated, solid lignin products as starting material for the process. Itis also possible to make use of the black liquor as such and to causethe lignin contained therein after oxidation to react at a suitable pHwith a sulphite or formaldehyde-sulphite addition compound or with both,whereupon the sulphonated, water soluble lignin product thus produced isfreed from the other constituents of the liquor, for example bydialysis.

The sulphonated lignin products produced according to the inventionpossess with regard to their composition a certain resemblance to thelignin sulphonic acids, which are obtained in the sulphite celluloseprocess. However, in several respects, characteristic differences existbetween the two kinds of lignin sulphonic acids. The lignin sulphonicacids of the sulphite waste liquor are comparativelyhigh-molecular-their average molecular weight is about 10,000and theycontain only very few phenolic hydroxyl groups. On the other hand, thesulphonic acids produced according to the present invention, arerelatively low-molecular-their molecule weight is 1000- 3000--and theycontain in conformity with the starting material comparatively many freephenolic hydroxyl groups.

Owing to these properties, the sulphonic acid derivatives of blackliquor lignin produced according to the invention are excellent tanningagents. Tanning tests have proved that they have a high afllnity for thehide, and that theycontrary to lignin sulphonic acids from sulphitewaste liquor-give a soft leather with increased shrinking temperature.Other purposes of utilization for which the products of the presentinvention are adapted are, for example, as emulsitying and dispersingagent, for example in the production of printing inks and cutting anddrilling oils, an s in e yemg asT'em' I g fillers for caoutchouc and asdispersing,

I u Especially favourable resu s are otained by employing black liquorlignin from the sulphate cellulose process, hereafter called sulphateblack liquor lignin, which to its character in certain respects isdifferent from black liquor lignin obtained by digesting wood withsolely alkali, the so-called soda black liquor lignin." Owing to thepresence of sulphides in the alkaline cooking liquor the lignin isdissolved from the wood more readily than is the case in the purealkaline process (the soda process). This has been explained by theassumption that the sulphide present in the cooking liquor reacts withbenzyl alcohol and benzyl ether groups in the lignin, converting theminto mercaptan groups, part of which may subsequently be furtherconverted, under the action of the alkali of the cooking liquor, intoketo groups. In this way the highly reactive benzyl alcohol and benzylether groups mentioned are deactivated. In the soda process, however,these groups give rise to condensation reactions resulting inhigh-molecular lignin products which are removed from the pulp only byprolonged cooking with the alkaline liquor or by the use of a highercooking temperature. The sulphate black liquor lignin may therefore beconsidered as a lignin product produced under milder conditions than thesoda black liquor lignin and in accordance herewith sulphate blackliquor llgn'in reacts more readily with sulphites in the sulphonatingprocess.

Another consequence of the condensation-preventing infiuence of thesulphide upon the dissolution of the lignin from the wood is that thesulphate black liquor lignin has a relatively lower and more uniformmolecular weight than the soda lignin. Thus, the molecular weight ofsulphate black liquor lignin is 1000-2000, consequently of the sameorder of magnitude as that of the most important vegetable tanningagents, and this fact may be a contributing cause to the especially goodtanning properties which the water-soluble products produced fromsulphate black liquor lignin according to the present invention haveproved to possess.

Example 1 200 gs. sulphate black liquor lignin were dissolved in asolution of 2' 2 gs. sodium hydroxide in 1 liter water and the solutionwas boiled for 12 hours under reflux While passing oxygen therethmugh.After this treatment the lignin could be precipitated by acidifying withacetic acid. When analysed by potentiometric titration it proved tocontain strong acid groups (sulphonic acid groups), although not in asufficient quantity for obtaining the desired solubility in water andacids. In order to obtain a sufliciently high content of sulphonic acidgroups, 50 gs. sodium sulphite (anhydrous) were added to the solutionpreviously oxidized as described, whereupon the solution was heated for3 hours at 150 C. The solution was then dialysed, until it was free fromsulphite ions, and was thereupon evaporated. The product thus obtainedcontained 8.8% SO3H and was readily soluble in water and dilute aceticacid' In order to obtain the same sulphonic acid content when using notpreviously oxidized sulphate black liquor lignin, it was necessary touse .100 gs. sodium sulphite, the conditions in other respects beinganalogous. The product had a high afiinity for hide. Its content oftanning substance was 78%.

Example 2 50 gs. lignin product, produced according to Example 1, wereheated for '6 hours at 100 C. in a solution of 50 gs. NazSOs and 25 ml.formaldehyde (40%) in 500 ml. water. The product obtained after dialysisand evaporation had a high content of sulphonic acid and could not beprecipitated from its aqueous solution with dilute mineral acid.

Example 4 50 gs. lignin product, produced according to Example 2, weredissolved in 500 mL'sodium i hydroxide (1%) and was reacted with 20 gs.

formaldehyde-bisulphite addition product by heating for 6 hours at 100C. The solution was worked up as in the preceding example.

6 Example 5 A solution of 200 gs. sulphate black liquor lignin and 20gs. sodium hydroxide in 2 liters water was heated for '6 hours at 100 C.while conducting air through the solution. Hereupon 100 gs.formaldehyde-bisulphite addition compound were added, whereupon thesolution-without conducting air therethrough wa's heated for further 6hours at 100 C.

What is claimed is:

1. In the manufacture of water-soluble products from lignin materials,the process which comprises sulfona'ting black liquor lignin bysubjecting it to the action of a sulfonating agent, selected from theclass consisting of sulfurous acid and water-soluble salts of sulfurousacid, also subjecting said lignin to an oxidizing treatment with anoxidizing gas, selected from the class consisting of air and oxygen,prior to completion of the sulfonating step, and recovering theresulting water-soluble sulfonated lignin product.

2. The process of claim 1 wherein the oxidizing treatment .is conductedprior to the sulfonating treatment.

3. The process of claim 1 wherein the oxidizing treatment is .conductedsimultaneously with the sulfonating treatment.

4. The method of claim 1 wherein the oxidizing and sulphonatingtreatments are carried out in alkaline solution.

5. The method of claim 1 wherein the oxidizing treatment is carried outby conducting the oxidizing gas into an alkaline solution of blackliquor lignin at boiling temperature.

6. The method of claim '1 wherein the sulphonating treatment is carriedout at a temperature within the range of to 200 C.

7. In the production of water-soluble products from lignin materials,the process which comprises subjecting black liquor lignin to anoxidizing treatment by contacting it with an oxidizing gas, selectedfrom the class consisting of air and oxygen, and to a sulphonation, withi an agent selected from the group consisting of sulfurous acid andwater-soluble salts thereof,

in combination with a treatment with an aldehyde, the oxidizingtreatment being completed before the aldehyde treatment and prior tocompletion of the sulphonation.

8. The method of claim 7 wherein the black liquor lignin is firstsubjected to said oxidizing and sulphonating treatments and then to thetreatment with an aldehyde.

9. The method of claim 7 wherein the black liquor is first subjected tosaid oxidizing treatment and then to said sulphonation whereupon theproduct thus obtained is reacted with an aldehyde.

10. The method of claim 7 wherein the black liquor is first subjected tosaid oxidizing and sulphonating treatments whereupon the product thusobtained is reacted with a mixture of a sulphonating agent and analdehyde.

11. The method of claim '7 wherein the black liquor is first subjectedto said oxidizing treatment and then reacted with a mixture of asulphonating agent and an aldehyde whereupon the product thus obtainedis subsequently subjected to a further sulphonation.

12. The method of claim 7 wherein the said aldehyde is formaldehyde.

13. The method of claim 7 wherein the oxidizing treatment is carried outin alkaline solution.

14. The method of producing water-soluble lignin products suitable foruse as taming agents, emulsifying and dispersing agents, textileassistants, reinforcing fillers in caoutchouc and for similar purposes,which comprises oxidizing black liquor lignin, by contacting it with agas, selected from the class consisting of air and oxygen, reacting theoxidized lignin at increased temperature with a sulphonating agentselected from the group consisting of sulphurous acid and water-solublesalts thereof, in order to introduce sulphonic acid groups into thelignin molecule, whereby the lignin is converted into water-solublestate, and then recovering the water-soluble lignin products thusobtained.

15. A method for producing water-soluble lignin products suitable foruse as tanning agents, emulsifying and dispersing agents, textileassistants, reinforcing fillers in caoutchouc and for similar purposes,which comprises heating black liquor lignin while treating itsimultaneously with an oxidizing agent, selected from the classconsisting of air and oxygen, and a sulphonating agent selected from thegroup consisting of sulphurous acid and water-soluble salts thereof,reacting the product thus obtained with an aldehyde to producewater-soluble sulphonic acid derivatives of the lignin, and thenrecovering the water-soluble products thus obtained.

16. A method for producing water-soluble lignin products suitable foruse as tanning agents, emulsifying and dispersing agents, textileassistants, reinforcing fillers in caoutchouc and for similar purposes,which comprises dissolving sulphate black liquor lignin in an alkalinesolution of sodium sulphite, passing an oxygencontaining gas, selectedfrom the class consisting of air and oxygen, through the solution atelevated temperature, heating the solution thustreated at a temperaturewithin the range of 50 to 200 C. to convert the lignin into watersolublesulphonic acid derivatives, and then re covering the water-solubleproduct thus produced.

17. A method for producing water-soluble lignin products suitable foruse as tanning agents, emulsifying and dispersing agents, textileassistants, reinforcing fillers in caoutchouc and for similar purposes,which comprises dissolving black liquor lignin in an alkaline solutionof sodium sulphite, boiling the solution under reflux to producesulfonation of the lignin while passing an oxygen-containing gas,selected from the class consisting of air and oxygen, therethrough,adding formaldehyde to the solution,

heating the solution thus obtained to convert the lignin intowater-soluble sulphonic acid derivatives, and then recovering thewater-soluble products thus produced.

18. A method for producing water-soluble lignin products suitable foruse as tanning agents, emulsifying and dispersing agents, textileassistants, reinforcing fillers in caoutchouc and for similar purposes,which comprises dissolving sulphate black liquor lignin in an alkalinesolution of sodium sulphite, heating the solution while passing anoxygen-containing gas, selected from the class consisting of air andoxygen, therethrough, to convert the lignin into watersoluble sulphonicacid derivatives, and removing low-molecular water-soluble productspresent by dialysis.

19. A method for producing water-soluble lignin products suitable foruse as tanning agents, emulsifying and dispersing agents, textileassistants, reinforcing fillers in caoutchouc and for similar purposes,which comprises mixing sulphate black liquor with an alkaline solutionof sodium sulphite, heating the mixture while passing anoxygen-containing gas, selected from the class consisting of air andoxygen, therethrough, adding formaldehyde and again heating to convertthe lignin into water-soluble sulphonic acid derivatives, removinglow-molecular substances from the sulfonated products by dialysis, andthen removing water-insoluble byproducts by filtration.

References Cited in the file Of this patent OTHER REFERENCES Paper TradeJournal, Oct. 12, 1950. Pages 30, 32, 33, 34.

Ser. 314,568, Rieche et al. (A. P. C.) published June 8, 1943.

1. IN THE MANUFACTURE OF WATER-SOLUBLE PRODUCTS FROM LIGNIN MATERIALS,THE PROCESS WHICH COMPRISES SULFONATING BLACK LIQUID LIGNIN BYSUBJECTING IT TO THE ACTION OF A SULFONATING AGENT, SELECTED FROM THECLASS CONSISTING OF SULFUROUS ACID AND WATER-SOLYBLE SALTS OF SULFUROUSACID, ALSO SUBJECTING SAID LIGNIN TO AN OXIDIZING TREATMENT WITH ANOXIDIZING GAS, SELECTED FROM THE CLASS CONSISTING OF AIR AND OXYGEN,PRIOR TO COMPLETION OF THE SULFONATING STEP, AND RECOVERING THERESULTING WATER-SOLUBLE SULFONATED LIGNIN PRODUCT.